A mechanical oil pump that operates in connection with a driving shaft of an engine is used in an automatic transmission vehicle in the related art. As the mechanical oil pump supplies excessive oil to a low-pressure unit requiring lubrication and a high-pressure unit that operates combination elements in a region where an RPM of the engine is high, the power of the mechanical oil pump may be wasted.
In recent years, an Idle Stop & Go (ISG) system, that stops the engine while the vehicle stops, has been applied in order to improve fuel efficiency. An electric oil pump for supplying hydraulic pressure to the automatic transmission is additionally mounted on the vehicle adopting the ISG system.
Furthermore, the mechanical oil pump that may cause the fuel efficiency to be degraded is deleted, and systems that supply oil to the transmission by only the electric oil pump have been developed.
In the system in which the oil is supplied to the transmission only by the electric oil pump, the electric oil pump is driven at the same time when the engine starts to supply oil to the low-pressure unit and the high-pressure unit.
However, if the engine starts, even in a stop state in which a shift lever maintains a parking shift stage (P stage) or a neutral shift stage (N STAGE), when the electric oil pump is continuously driven, power loss may be caused by unnecessary driving of the oil pump. Further, the unnecessary driving of the electric oil pump may degrade durability of the combination elements provided in the electric oil pump, the automatic transmission, and the electric oil pump. In addition, noise may be generated by the unnecessary driving of the electric oil pump.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.